Certain conventional non-mechanical microfluidic pumps utilize a series of pump heating elements fabricated on the substrate within a fluid transport channel to generate thermal vapor bubbles. The bubbles are typically created either at nucleation sites by raising the overall temperature of the fluid to the boiling point or by supercritical heating of a small portion of the fluid around the heating element to a temperature above the boiling point without significantly raising the overall fluid temperature. By sequencing the activation of the pump heating elements, the fluid flow is controlled.
Conventional microfluidic pumps employing thermal vapor bubbles to transport fluids rely on passive cooling to dissipate the heat generated during the creation of the thermal vapor bubbles. The rate of heat dissipation is determined by the volume, surface area, and thermal conductivity of conventional microfluidic pump components (e.g., the substrate) in thermal communication with the pump heating elements and the fluid. Conventional microfluidic pumps are designed with a heat dissipation rate intended to sufficiently cool the microfluidic pump and fluid when operating within a certain range of conditions (e.g., ambient temperature) at typical utilization levels with certain fluids. However, the designed heat dissipation rate is not always appropriate to accommodate the variations conditions, utilizations, and fluid compositions that are encountered.
If the passive cooling system is insufficient to dissipate the generated heat, the overall temperature of the fluid will rise over time as operation continues. In many cases, heating a fluid above a certain temperature has undesirable effects on the fluid composition (e.g., concentration of the fluid) or characteristics (e.g., reduced viscosity) that make the fluid unsuitable for a particular application or otherwise adversely affect the performance of the fluid (e.g., overspray or adherence) and, potentially, the microfluidic pump. At the same time, passive cooling system designs with higher heat dissipation rates may remove too much heat from the microfluidic pump preventing the fluid from reaching a minimum operating temperature in certain conditions, which may also adversely affect the characteristics (e.g., low flowability) or performance (e.g., poor dispersion or clumping) of the fluid and, potentially, the microfluidic pump. It is with respect to these and other consideration that the present invention was conceived.